<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="jquery.min.js"></script>
</head>
<body>
    <button>1</button>
    <button>1</button>
    <button>1</button>
    <button>1</button>
    <button>1</button>
    <button>1</button>

    <script>
        $(function(){
            $("button").click(function(){
             
                // $("button").css('background','')
                $(this).css('background','pink')
                $(this).siblings("button").css('background','')
            })
        })
    </script>
</body>
</html>